Tires have been filled for a number of years, with a number of types of materials, by varying processes as disclosed in a number of U.S. patents. Most of these materials and processes, however, have serious drawbacks in actual practice.
The most successful, and the most widely used at present, presenting fewer drawbacks than other methods, is that shown in U.S. Pat. No. 3,866,651. This is a solid polyurethane elastomer system. With this system, cost and weight are the major drawbacks, plus the fact that these tires are limited to rather low continuous speeds. These drawbacks limit the market for this system mostly to industrial vehicles where flat tires constitute serious delays in time consumed in changing tires. The end product is excellent for the use for which it is intended, but has the above-noted limitations in market development into other types of vehicle tires.
U.S. Pat. No. 3,022,810 shows a polyurethane foam system, blown with compressed air. Other U.S. Pat. Nos. such as 3,854,516 and 3,605,848 also describe polyurethane foam compounds for filling tires. These systems have been tried on a limited scale, but have not been successful, since the foam could not be controlled accurately to match the load-bearing properties for the different pressures the tires were designed for. The wide range of tires on the market are designed for pressures from some 10 PSI on through 120 PSI, and load bearing characteristics must match the pneumatic pressures. Another major drawback in these systems is that the foam could not be placed in the tires in such a manner that equal densities could be had throughout the tire, and usually densities were greater at the fill point than at the bleed point, resulting in tires which were seriously out of balance and with one side of the tire having higher load-bearing properties than the opposite side. U.S. Pat. No. 3,854,516 tries to eliminate this last problem by rotating the tire while filling, and at the same time using this motion to mix the ingredients making up the foam material, but due to the nature of polyurethane foam, cell structure will collapse if any appreciable motion occurs during a critical period of the rise and gel of the foam, so by trying to eliminate one problem, another problem was created.
Other patents, as well as the above-mentioned, have tried both open cell foam and closed cell foam for the filling of tires. U.S. Pat. No. 3,605,848 entails open-cell foam, while U.S. Pat. No. 3,022,810 entails closed cell foam. Open cell foam has the disadvantage of creating excess flexural heat during operation of the tire, even at relatively low speeds, which seriously empair tire life due to fatigue and deterioration of the polyurethane. Other U.S. patents relating to filled tires include U.S. Pat. Nos. 3,994,329; 3,987,832; 3,915,774, 3,907,018; 3,872,201; 3,494,607; 3,381,735; 3,331,423; 3,208,497; 3,112,785; 3,952,786; 3,866,652; 3,646,983; 3,256,123; 3,179,148; and 3,095,917.
To date, and to our knowledge, no one else has been successful in formulating a polyurethane foam and filling an object with a resilient, flexible polyurethane foam with high (over 90%) closed cells which would not shrink and deform during the curing process. We believe we have the only existing system by which tires of any given size and pressure ratings may be successfully filled accurately and fully balanced, to match the intended pressure ratings from some 10 PSI on through 120 PSI with good handling characteristics and good tire wear life.